1. Field of the Invention
The present invention relates in general to brushless motors and more particularly to brushless motors of a type which exhibits a satisfied heat proof performance and is easy to be assembled.
2. Description of the Prior Art
In order to clarify the task of the present invention, two conventional brushless motors will be briefly described with reference to FIGS. 16 and 17 of the accompanying drawings.
In FIG. 16, there is shown one conventional brushless motor 100. The motor 100 comprises a drive circuit 102 for driving a motor shaft 104. The drive circuit 102 generally comprises a filter section which filters out surges from a supplied electric power, a switching section which switches the path of the current from the filter section toward a stator 106 thereby to vary the magnetic fields generated by the stator 106 and a control section which controls rotation of the motor shaft 104 by controlling the switching timing of the switching section. These sections of the drive circuit 102 are all arranged on a circuit substrate 108. The circuit substrate 108 is accommodated in a circuit protection case 110.
The switching section comprises a plurality of switching elements 112 which switch the path of current directed to coils 114 of the stator 106, and the control section comprises electronic parts 107 which control the switching timing of the switching elements 112. Since the switching elements 112 produce a considerable amount of heat under operation, these elements 112 are attached to a heat sink 115 which is formed with a plurality of heat radiation fins 116. That is, under operation of the motor 100, the heat generated by the switching elements 112 is transmitted to the heat sink 115 and released to the open air by the heat radiation fins 116.
However, hitherto, it has been difficult to effectively release the heat of the switching elements 112 to the open air. In fact, if the motor 100 is designed to generate a higher output, the switching elements 112 are forced to generate a marked heat inevitably and thus it becomes necessary to use high heat-proof and thus expensive ones as the electronic parts 107 of the control section of the drive circuit 102.
In FIG. 17, there is shown the other conventional brushless motor 200 which is shown in Laid-open Japanese Patent Publication 9-191625. The motor 200 comprises a drive circuit 202 for driving a motor shaft 204. The drive circuit 202 is accommodated in a circuit protection case 210. The drive circuit 202 is printed on a circuit substrate 212, and generally comprises a filter section 202a which filters our surges from a supplied power, and a control section 202b which controls magnetic fields of a stator 214 by switching the path of the current from the filter section 202a at given intervals. The control section 202b comprises a plurality of switching elements 216 which switch the path of current directed to coils 214a of the stator 214. The switching elements 216 are attached to a heat sink 218 formed with a plurality of heat radiation fins 218a. Thus, under operation of the motor 200, the heat generated by the switching elements 216 is transmitted to the heat sink 218 and released to the open air from the heat radiation fins 218a. 
The coils 214a of the stator 214 and the control section 202b of the drive circuit 202 are connected through terminal pins 220 which extend from the coils 214a to bus bars 224 which, in turn are connected to joint bars 222 held by the circuit substrate 212.
However, employment of the terminal pins 220, joint bars 222 and bus bars 224 for connecting the control section 202b to the coils 214a has caused a troublesome and time-consuming work for assembling the motor 200. For example, for welding given portions of the bus bars 224 to the joint bars 222 and the terminal pins 220, it is necessary to precisely hold the bus bars 224 at given positions before carrying out the welding work.
It is therefore an object of the present invention to provide a brushless motor which is free of the above-mentioned drawbacks.
According to the present invention, there is provided a brushless motor which is constructed to suppress or at least minimize undesired heat transmission from a heat generating switching section of a drive circuit to a control section of the same.
According to the present invention, there is further provided a brushless motor which is easily assembled.
According to the present invention, there is provided a brushless motor which comprises a circuit protecting case; a holder disposed on the case; a motor shaft rotatably held by the holder; a stator disposed about the holder, the stator including a plurality of coils which surround the motor shaft; a yoke fixed to the motor shaft to rotate therewith, the yoke covering the stator with a given space therebetween; permanent magnets held by the yoke; a circuit substrate tightly held in the circuit protecting case; a drive circuit arranged on the circuit substrate, the drive circuit including a switching section which switches the path of current directed to the coils of the stator and a control section which controls a switching timing of the switching section, the switching section including a plurality of switching elements which generate a certain heat when operated; and a partition wall provided in the circuit protection case to partition the interior of the case into a first chamber to which the switching elements of the switching section are exposed and a second chamber to which the control section is exposed.